Coiled tubing self-retracting which fluids may pass under high pressure have been known for some time and have been utilized in conjunction with pneumatic equipment. The use of coiled flexible and self-retracting tubing eliminates the need for reels or counterbalances for retracting or storing the tubing when the equipment is not in use. Various devices have been suggested to maintain the tubing in its coiled form, and these include devices which are applied to the exterior of the tubing. Alternatively, it is possible to prepare tubing in a coiled form wherein wire is molded into the rubber or plastic tubing in order to provide additional recoil strength to a coil formed from the tubing which is above and beyond that strength which can be obtained from the rubber or plastic by itself. Incorporation of such wires has not resolved the problems completely since the wires have a tendency to break through continued use of the tubing.
Although the desirability of eliminating externally applied devices or wire reinforcements has been appreciated for some time, few rubbery or plastic materials have been known which can be utilized in the preparation of coiled tubing having the desirable recoil strengths. U.S. Pat. No. 3,021,871 describes a coiled nylon tubing which is useful for transmitting fluids under pressure to pneumatic equipment and which exhibits the desirable recoil properties. It is suggested therein that coiled tubing made of other existing plastics such as polyvinyl chloride, polyethylene, polystyrene, and the like, do not exhibit the desirable characteristics or possess sufficient elastic memory to be acceptable. For example, polystyrene, though quite pliable, reportedly does not have sufficient stiffness to provide the necessary resilience to the coiled shape, and none of the three plastics mentioned had sufficient tensile strength to withstand the necessary operating pressures of a tubing using a practical wall thickness.
Studies involving the potential application of other types of plastic materials, both new and old, or combinations thereof, have continued in an effort to develop plastic materials which would be useful as tubing materials and particularly as coiled tubing exhibiting the desirable recoil strength and memory. The invention of this application relates to such a discovery.